How to mix 2 textures using different UV maps on one object
I figured things out. I don't really understand why it works, but i was able to resolve my problem by inputting alpha of one of the textures into "Mix shader" factor.

This is a easy stuff, but i didn't expect it to work, because my UV sets are very different, and if merged together will interpenetrate each other and create a mess, so i didn't consider doing alpha of one of my textures as a mask.